If the USB drive is not recognized by the PC, try the following action;
a) Change the USB cable or USB port and reconnect it.
b) Make sure the connection of the power and the connect, and reconnect them.

Format the USB drive to NTFS.

Only the USB drive formatted by NTFS can be recognized by the CloudStation.

Our USB drive can't be recognized when you connect it to the CloudStation right after you open the package due to the default format type of our USB drive products is FAT32.

The USB drive needs to be formatted to NTFS before you connect it to the CloudStation.
Refer to the Answers for how to format the USB drive.